ᐅ How does the indoor climate affect the stability of Malm stone?

Hello everyone,

I am currently looking into the question: How does the indoor climate affect the stability of Malm? Malm – especially as a limestone layer – is used in various fields, for example in the construction industry and also for underground climate protection. I understand that temperature, humidity, and air circulation significantly influence the indoor climate, but to what extent do these factors specifically affect the structural stability and weathering behavior of Malm? Are there any particular aspects to consider when planning to use or store Malm over the long term? I look forward to your insights and experiences.

Hello nepe51,

To answer your question thoroughly: The indoor climate mainly affects the stability of Malm through temperature and humidity fluctuations. Malm, as a limestone-containing stone, is particularly susceptible to physical and chemical weathering.

1. Moisture increases water absorption, which can lead to volume changes – the alternating expansion and contraction can create stress.
2. Temperature changes, especially freeze-thaw cycles, cause microcracks.
3. A high CO2 concentration in the air can lead to increased carbonation processes, which attack the surface.

As a tip: Maintaining a constant indoor humidity of about 50-60% and a stable temperature around 20°C (68°F) is optimal to largely preserve the original stability.

nepe51 schrieb:
die strukturelle Stabilität und das Verwitterungsverhalten von Malm

These two aspects are closely linked – as weathering progresses, the structural stability automatically decreases.

In short: High humidity and temperature fluctuations make marl brittle and unstable. Dry and stable conditions are preferable.

In addition to the previous explanations: Malm has porous and carbonate-containing properties. The indoor climate particularly affects the dissolution processes of calcium carbonate. At high humidity levels, the chemical solubility increases, often influenced by acidic gases in the air (such as CO2). Over time, this can lead to cavities and micro-defects that compromise stability. Another factor is capillary action, which draws moisture into the stone and thereby creates internal stresses.

For proper storage or use, monitoring both the relative humidity and the temperature is recommended.

I appreciate that the practical side is also addressed here. I once had a similar issue with a small construction project using Malm building components. The humidity levels were not properly monitored, and after some time, the first cracks appeared. It is frustrating when you work with a seemingly solid material and something like that happens.

I wonder how strictly the recommendations for indoor climate parameters are followed in practice and whether there are standards that can be easily implemented. Who has experience with this? Especially when using Malm, for example, in interior walls, it is not always possible to continuously control the climate.

FELOTAU schrieb:
It is frustrating when you work with a seemingly solid material and then something like this happens.

That’s true, especially since Malm is often trusted as a natural stone. One issue I consider very important is the underestimation of microclimates. Even if the general indoor climate is controlled, areas like corners or places with poor air circulation tend to be more vulnerable to higher humidity.

nepe51 schrieb:
Are there any special considerations to keep in mind if you want to use or store Malm long-term?

Here, I would emphasize that Malm should ideally not come into direct contact with water or sources of water vapor (e.g., bathrooms, utility rooms). Additionally, good ventilation is recommended for storage facilities to minimize condensation.